Measurements of the proton elastic-form-factor ratio μpGEp/GMp at low momentum transfer

G. Ron*, J. Glister, B. Lee, K. Allada, W. Armstrong, J. Arrington, A. Beck, F. Benmokhtar, B. L. Berman, W. Boeglin, E. Brash, A. Camsonne, J. Calarco, J. P. Chen, Seonho Choi, E. Chudakov, L. Coman, B. Craver, F. Cusanno, J. DumasC. Dutta, R. Feuerbach, A. Freyberger, S. Frullani, F. Garibaldi, R. Gilman, O. Hansen, D. W. Higinbotham, T. Holmstrom, C. E. Hyde, H. Ibrahim, Y. Ilieva, C. W. De Jager, X. Jiang, M. K. Jones, H. Kang, A. Kelleher, E. Khrosinkova, E. Kuchina, G. Kumbartzki, J. J. Lerose, R. Lindgren, P. Markowitz, S. May-Tal Beck, E. McCullough, D. Meekins, M. Meziane, Z. E. Meziani, R. Michaels, B. Moffit, B. E. Norum, Y. Oh, M. Olson, M. Paolone, K. Paschke, C. F. Perdrisat, E. Piasetzky, M. Potokar, R. Pomatsalyuk, I. Pomerantz, A. Puckett, V. Punjabi, X. Qian, Y. Qiang, R. Ransome, M. Reyhan, J. Roche, Y. Rousseau, A. Saha, A. J. Sarty, B. Sawatzky, E. Schulte, M. Shabestari, A. Shahinyan, R. Shneor, S. Širca, K. Slifer, P. Solvignon, J. Song, R. Sparks, R. Subedi, S. Strauch, G. M. Urciuoli, K. Wang, B. Wojtsekhowski, X. Yan, H. Yao, X. Zhan, X. Zhu

*Corresponding author for this work

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53 Scopus citations


High-precision measurements of the proton elastic form-factor ratio, μpGEp/GMp, have been made at four-momentum transfer, Q2, values between 0.2 and 0.5GeV2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q2 range the deviation from unity is primarily due to GEp being smaller than expected.

Original languageAmerican English
Article number202002
JournalPhysical Review Letters
Issue number20
StatePublished - 13 Nov 2007
Externally publishedYes


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